The core Java fundamentals that we are about to learn apply when working within classes that we inherit from (such as Activity/AppCompatActivity), as well as classes that we write ourselves (as we will start to do in Chapter 10, Object-Oriented Programming).
As it is more logical to learn the basics before we write our own classes, we will be using the extended Activity class, AppCompatActivity, to add lots of different code in a whole bunch of mini-projects in the next few chapters to learn and practice Java. We will use Log and Toast again to see the results of our coding. In addition, we will use more methods that we will write ourselves (called from buttons), as well as the overridden methods of the Activity class to trigger the execution of our code. We will finally get the full details on methods in Chapter 9, Java Methods.
When, however, we move onto Chapter 10, Object-Oriented Programming, and start to write our own classes, as well as understand more about how...